Somatomedin C/insulin-like Growth Factor I levels after treatment of acromegaly

An in-house method was used, including dissociation of Somatomedin C/insulin-like Growth Factor I (Sm-C/IGF-I) binding proteins with acid and extraction of Sm-C/IGF-I by C-2 cartridge before radioimmunoassay, to measure plasma Sm-C/IGF-I levels in three groups of patients - total of 19 - with acromegaly who underwent transsphenoidal removal of pituitary tumors. In group A (n = 7), the Sm-C/IGF-I levels did not decrease to normal on postoperative day 1 even though the growth hormone concentration had decreased to normal. In group B (n = 4), the Sm-C/IGF-I level decreased to normal in three of the four patients on postoperative day 4, but it remained elevated in one. At two months postoperatively, all four patients had normal values. Group C patients (n = 8) had had an operation two to 23 years previously, and all remained in remission with normal Sm-C/IGF-I levels. Our findings indicate that the Sm-C/IGF-I assay is useful for monitoring acromegaly after transsphenoidal removal of pituitary tumors, but it should be ordered at least four days postoperatively.